Refrigerating machine oil composition for natural refrigerant

ABSTRACT

This invention describes a refrigerating oil composition for natural substance-based refrigerants which comprises (A) a synthetic oil component comprising a polyether compound having a pour point of −10° C. or lower and (B) a mineral oil component comprising sulfur components, wherein the ratio of amounts by weight of component (A) to component (B) is in the range of 25:75 to 99:1 and the amount of the sulfur components derived from component (B) in the composition is in the range of 5 to 1,000 ppm. The refrigerating oil composition has excellent miscibility with natural substance-based refrigerants and, in particular, with ammonia-based refrigerants, exhibits an improved lubricity and used for industrial refrigerators using natural substance-based refrigerants such as ammonia, propane, butane and carbon dioxide.

TECHNICAL FIELD

The present invention relates to a refrigerating oil composition fornatural substance-based refrigerants and, more particularly, to arefrigerating oil composition which can be used for industrialrefrigerators using natural substance-based refrigerants such asammonia, propane, butane and carbon dioxide.

BACKGROUND ART

In general, refrigerators such as compression-type refrigeratorscomprising a compressor, a condenser, an expansion valve and anevaporator have a structure in which a mixed fluid of a refrigerant anda lubricating oil is circulated in the closed system. Heretofore,chlorofluorocarbons such as dichlorodifluoromethane (R-12) andchlorodifluoromethane (R-22) have been used as the refrigerant for thecompression-type refrigerators and various types of lubricating oilshave been produced and used in combination with the refrigerant.However, since there is the anxiety that the chlorofluorocarbons causeenvironmental pollution such as ozonosphere destruction in stratospherewhen these substances are released into the atmosphere, the regulationon the chlorofluoro-carbons is becoming stricter worldwide. Due to thissituation, novel refrigerants such as hydrofluorocarbons andfluorocarbons, typical examples of which include1,1,1,2-tetrafluoroethane (R-134a), are attracting attention. Althoughthere is no anxiety that the hydrofluorocarbons and the fluorocarbonsdestruct the ozonosphere, there is the fear that these substances mightcause global warming due to the longevity of these substances in theatmosphere. Therefore, the use of natural substance-based refrigerantsthat do not cause the above problems is considered.

Among the natural substance-based refrigerants, ammonia has heretoforebeen used for industrial refrigerators that require oil agents andrefrigerants in great amounts. As the refrigerating oil for suchrefrigerators, mineral oils have been used. However, since mineral oilsand ammonia are not miscible with each other, additional apparatusessuch as an apparatus for separation of the oil are indispensable.Therefore, the system becomes great and, moreover, the performance ofthe system is not sufficiently satisfactory.

In Japanese Patent Application Laid-Open No. Heisei 5(1993)-9483, it isdisclosed that polyalkylene glycols which do not have hydroxyl group atany of the ends have excellent miscibility with ammonia and contributeto improvement in the performance to a great extent. It is described inthe specification of the above application that additives conventionallyused for refrigerating oils such as extreme pressure agents andantioxidants can be used. However, the use of the additives is not shownin the examples.

In Japanese Patent Application Laid-Open No. Heisei 6(1994)-10081,additives advantageously used in combination with ammonia orhydrofluorocarbon refrigerants are disclosed. However, the use of theadditives specifically described in the examples is limited to the usein combination with hydrofluorocarbon refrigerants.

In general, since ammonia has a greater reactivity than otherrefrigerants and exhibits basic property by itself, acidic substanceshave been considered to be unsuitable for use in combination withammonia. On the other hand, most of the additives are actually acidicsubstances. This situation causes insufficient lubrication and theimprovement has been desired. The present situation described above isreflected on the fact that the above references have no specificdescriptions on the use of combinations of ammonia with conventionaladditives. It has not been found whether the combinations can be usedfor practical applications.

The present invention has an object of providing a refrigerating oilcomposition having excellent miscibility with natural substance-basedrefrigerants and, in particular, with ammonia-based refrigerants andexhibiting an improved lubricity.

As the result of extensive studies by the present inventors, it wasfound that the object of the present invention could be effectivelyachieved when the refrigerating oil composition comprises a syntheticoil component comprising a polyether compound having a specific propertyand a mineral oil component comprising sulfur in specific relativeamounts, and the amount of the sulfur components is in the range of 5 to1,000 ppm in the composition. The present invention has been completedbased on this finding.

DISCLOSURE OF THE INVENTION

The refrigerating oil composition for natural substance-basedrefrigerants of the present invention has the following aspects:

-   (I) A refrigerating oil composition for natural substance-based    refrigerants which comprises (A) a synthetic oil component    comprising a polyether compound having a pour point of −10° C. or    lower and (B) a mineral oil component comprising sulfur components,    wherein (A):(B) which is a ratio of an amount by weight of    component (A) to an amount by weight of component (B) is in a range    of 25:75 to 99:1 and an amount of the sulfur components derived from    component (B) in the composition is in a range of 5 to 1,000 ppm;-   (II) A refrigerating oil composition for natural substance-based    refrigerants described in (I), wherein the polyether compound is a    polyalkylene glycol compound represented by general formula (1):    R¹—O-A-R²  (1)    wherein R¹ and R² each represent hydrogen atom or an alkyl group    having 1 to 4 carbon atoms, one of R¹ and R² represents an alkyl    group having 1 to 4 carbon atoms and an other of R¹ and R²    represents hydrogen atom; A represents a chain of a homopolymer of    propylene oxide or a copolymer of ethylene oxide and propylene    oxide; and, when a number of an ethylene oxide unit is represented    by m and a number of a propylene oxide unit is represented by n, m    and n satisfy following relations: 0≦m/n≦10 and 5≦m+n≦100;-   (III) A refrigerating oil composition for natural substance-based    refrigerants described in (I), wherein the polyether compound is a    polyvinyl ether compound; and-   (IV) A refrigerating oil composition for natural substance-based    refrigerants described in (I), wherein the natural substance-based    refrigerants comprises 90% by weight or more of ammonia.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows a flow diagram that exhibits an example of the compressiontype refrigerating cycle of the “compressor—condenser—expansionvalve—evaporator” system having an oil separator and a hot gas line.

FIG. 2 shows a flow diagram that exhibits an example of the compressiontype refrigerating cycle of the “compressor—condenser—expansionvalve—evaporator” system having an oil separator.

FIG. 3 shows a flow diagram that exhibits an example of the compressiontype refrigerating cycle of the “compressor—condenser—expansionvalve—evaporator” system having a hot gas line.

FIG. 4 shows a flow diagram which exhibits an example of the compressiontype refrigerating cycle of the “compressor—condenser—expansionvalve—evaporator” system.

Descriptions of the numerical symbols in the Figures are as thefollowings:

1: A compressor

2: A condenser

3: An expansion valve

4: An evaporator

5: An oil separator

6: A hot gas line

7: A valve for a hot gas line

THE MOST PREFERRED EMBODIMENT TO CARRY OUT THE INVENTION

It is necessary that the polyether compound used in the presentinvention have a pour point of −10° C. or lower. It is preferable thatthe kinematic viscosity at 100° C. is 3 to 50 mm²/s. It is morepreferable that the kinematic viscosity is 3 to 45 mm²/s and the pourpoint is −15° C. or lower. When the kinematic viscosity is lower than 3mm²/s, the lubricity is not sufficiently exhibited at high temperatures.When the kinematic viscosity exceeds 50 mm²/s, miscibility with ammoniamarkedly decreases and power loss increases. Therefore, the anxiety thatan efficient operation cannot be completed increases. When the pourpoint is higher than −10° C., resistance to flow at low temperatureincreases and efficiency and the lubricities are adversely affected.

The polyether compound used in the present invention is not particularlyspecified as long as the above requirements are satisfied. Polyalkyleneglycol compounds and polyvinyl ether compounds are suitable as thepolyether compound. Polyalkylene glycol compounds represented by theforegoing general formula (1) are more suitable as the polyalkyleneglycol compound.

In the foregoing general formula (1) representing the polyalkyleneglycol compound, R¹ and R² each represent hydrogen atom or an alkylgroup having 1 to 4 carbon atoms such as methyl group, ethyl group,n-propyl group, isopropyl group, n-butyl group, sec-butyl group,isobutyl group and tert-butyl group, one of R¹ and R² represents analkyl group having 1 to 4 carbon atoms and the other of R¹ and R²represents hydrogen atom. The compound may have various copolymerstructures such as structures of a block copolymer, a random copolymerand an alternating copolymer. m and n represent numbers satisfying thefollowing relations: 0≦m/n≦10, preferably 0≦m/n≦3 and more preferably0≦m/n≦2; and 5≦m+n≦100 and preferably 5≦m+n≦50.

In the present invention, apart from the polyalkylene glycol compoundrepresented by the foregoing general formula (1), a polyalkylene glycolcompound of an ethylene oxide-propylene oxide copolymer represented bythe following general formula (2):

can also be used as the polyether compounds. In the general formula (2),R³, R⁴ and R⁵ each represent hydrogen atom or an alkyl group having 1 to4 carbon atoms, at least one of R³, R⁴ and R⁵ represents an alkyl grouphaving 1 to 4 carbon atoms and A is the same as defined above forgeneral formula (1).

Examples of the alkyl group having 1 to 4 carbon atoms represented byR³, R⁴ or R⁵ in the general formula (2) include methyl group, ethylgroup, n-propyl group, isopropyl group, n-butyl group, sec-butyl group,isobutyl group and tert-butyl group. At least one of R³, R⁴ and R⁵represents an alkyl group having 1 to 4 carbon atoms. When the valuerepresented by m/n exceeds 10 in general formula (1) or (2) representingthe compound used for the refrigerating oil composition of the presentinvention, a drawback arises in that the compound becomes waxy and themiscibility becomes poor. When the value represented by m+n is smallerthan 5, a drawback arise in that the viscosity is excessively small andthe lubricity becomes poor. When the value represented by m+n exceeds100, a drawback arises in that the miscibility and the efficiency ofheat exchange become poor due to a high viscosity.

Examples of the polyvinyl ether compound include polyvinyl ethercompounds comprising constituting units represented by general formula(3):

wherein R⁵, R⁶ and R⁷ each represent hydrogen atom or a hydrocarbongroup having 1 to 8 carbon atoms, the atom and the groups represented byR⁵, R⁶ and R⁷ may be the same with or different from each other, R⁸represents a divalent hydrocarbon group having 1 to 10 carbon atoms, R⁹represents a hydrocarbon group having 1 to 20 carbon atoms, k representnumbers giving an average value of 0 to 10, the atom and the groupsrepresented by R⁵ to R⁹ may be the same or different among differentconstituting units and, when a plurality of R⁸O are present, theplurality of R⁸O may represent the same group or different groups.

Polyvinyl ether compounds comprising block or random copolymerscomprising the constituting units represented by the foregoing generalformula (3) and constituting units represented by the following generalformula (4):

can also be used as the polyether compounds. In the general formula (4),R¹⁰ to R¹³ each represent hydrogen atom or a hydrocarbon group having 1to 20 carbon atoms and the atom and the groups represented by R¹⁰ to R¹³may be the same with or different from each other and may be the same ordifferent among different constituting units.

In the foregoing general formula (3), R⁵, R⁶ and R⁷ each representhydrogen atom or a hydrocarbon group having 1 to 8 carbon atoms andpreferably 1 to 4 carbon atoms. The atom and the groups represented byR⁵, R⁶ and R⁷ may be the same with or different from each other.Examples of the hydrocarbon group include alkyl groups such as methylgroup, ethyl group, n-propyl group, isopropyl group, n-butyl group,isobutyl group, sec-butyl group, tert-butyl group, various types ofpentyl groups, various types of hexyl groups, various types of heptylgroups and various types of octyl groups; cycloalkyl groups such ascyclopentyl group, cyclohexyl group, various types of methylcyclohexylgroups, various types of ethylcyclohexyl groups and various types ofdimethylcyclohexyl groups; aryl groups such as phenyl group, varioustypes of methylphenyl groups, various types of ethylphenyl groups andvarious types of dimethylphenyl groups; and arylalkyl groups such asbenzyl group, various types of phenylethyl groups and various types ofmethylbenzyl groups. It is preferable that R⁵, R⁶ and R⁷ representhydrogen atom.

On the other hand, R⁸ in general formula (3) represents a divalenthydrocarbon group having 1 to 10 carbon atoms and preferably 2 to 10carbon atoms. Examples of the divalent hydrocarbon group having 1 to 10carbon atoms include divalent aliphatic groups such as methylene group,ethylene group, phenylethylene group, 1,2-propylene group,2-phenyl-1,2-propylene group, 1,3-propylene group, various types ofbutylene groups, various types of pentylene groups, various types ofhexylene groups, heptylene groups, various types of octylene groups,various types of nonylene groups and various types of decylene groups;alicyclic groups having two bonding portions on an alicyclic hydrocarbonsuch as cyclohexane, methyl-cyclohexane, ethylcyclohexane,dimethylcyclohexane and propylcyclo-hexane; divalent aromatichydrocarbon groups such as various types of phenylene groups, varioustypes of methylphenylene groups, various ethylphenylene groups, varioustypes of dimethylphenylene groups and various types of naphthylenegroups; alkylaromatic groups having one monovalent bonding portion oneach of the alkyl portion and the aromatic portion of alkylaromatichydrocarbons such as toluene, xylene and ethylbenzene; and alkylaromatichydrocarbon groups having bonding portions on alkyl group portions ofpolyalkylaromatic hydrocarbons such as xylene and diethylbenzene. Amongthe above groups, aliphatic groups having 2 to 4 carbon atoms arepreferable.

Further, k in general formula (3) represent numbers showing therepeating numbers of the group represented by R⁸O and giving an averagevalue in the range of 0 to 10 and preferably in the range of 0 to 5.When a plurality of R⁸O are present, the plurality of R⁸O may representthe same group or different groups.

Furthermore, R⁹ in general formula (3) represents a hydrocarbon grouphaving 1 to 20 carbon atoms and preferably 1 to 10 carbon atoms.Examples of the hydrocarbon group represented by R⁹ include alkyl groupssuch as methyl group, ethyl group, n-propyl group, isopropyl group,n-butyl group, isobutyl group, sec-butyl group, tert-butyl group,various types of pentyl groups, various types of hexyl groups, varioustypes of heptyl groups, various types of octyl groups, various types ofnonyl groups and various types of decyl groups; cycloalkyl groups suchas cyclopentyl group, cyclohexyl group, various types ofmethylcyclohexyl groups, various types of ethylcyclohexyl groups,various types of propylcyclohexyl groups and various types ofdimethylcyclohexyl groups; aryl groups such as phenyl group, varioustypes of methylphenyl groups, various types of ethylphenyl groups,various types of dimethylphenyl groups, various types of propylphenylgroups, various types of trimethylphenyl groups, various types ofbutylphenyl groups and various types of naphthyl groups; and arylalkylgroups such as benzyl group, various types of phenylethyl groups,various types of methylbenzyl groups, various types of phenylpropylgroups and various types of phenylbutyl groups. The atom and the groupsrepresented by R⁵ to R⁹ may be the same or different among differentconstituting units.

It is preferable that polyvinyl ether compound (i) comprising theconstituting units represented by the foregoing general formula (3) hasa ratio of the number by mole of carbon to the number by mole of oxygenin the range of 4.2 to 7.0. When this ratio is smaller than 4.2, thecompound is hygroscopic to a great extent. When the ratio exceeds 7.0,miscibility with the refrigerant occasionally becomes poor.

In the foregoing general formula (4), R¹⁰ to R¹³ each represent hydrogenatom or a hydrocarbon group having 1 to 20 carbon atoms and the atom andthe groups represented by R¹⁰ to R¹³ may be the same with or differentfrom each other. Examples of the hydrocarbon group having 1 to 20 carbonatoms include the groups described above as the examples of thehydrocarbon group represented by R⁹ in the foregoing general formula(3). The atom and the groups represented by R¹⁰ to R¹³ may be the sameor different among different constituting units.

It is preferable that polyvinyl ether compound (ii) comprising a blockor random copolymer comprising the constituting units represented bygeneral formula (3) and the constituting units represented by generalformula (4) has a ratio of the number by mole of carbon to the number bymole of oxygen in the range of 4.2 to 7.0. When this ratio is smallerthan 4.2, the compound is hygroscopic to a great extent. When the ratioexceeds 7.0, miscibility with the refrigerant occasionally becomes poor.

In the present invention, a mixture of the polyvinyl ether compound (i)and the polyvinyl ether compound (ii) may also be used. Polyvinyl ethercompounds (i) and (ii) used in the present invention can be produced bypolymerization of the corresponding vinyl ether monomer andcopolymerization of the corresponding hydrocarbon monomer having anolefinic double bond and the corresponding vinyl ether monomer,respectively.

As the polyvinyl ether compound used in the present invention, polyvinylether compounds having the following end structures are preferable:

Polyvinyl ether compounds that have one end having the structurerepresented by general formula (5) or (6):

wherein R¹⁴, R¹⁵ and R¹⁶ each represent hydrogen atom or a hydrocarbongroup having 1 to 8 carbon atoms, the atoms and the groups representedby R¹⁴, R¹⁵ and R¹⁶ may be the same with or different from each other,R¹⁹, R²⁰, R²¹ and R²² each represent hydrogen atom or a hydrocarbongroup having 1 to 20 carbon atom, the atoms and the groups representedby R¹⁹, R²⁰, R²¹ and R²² may be the same with or different from eachother, R¹⁷ represents a divalent hydrocarbon group having 1 to 10 carbonatoms, R¹⁸ represents a hydrocarbon group having 1 to 20 carbon atoms, prepresent numbers giving an average value of 0 to 10 and, when aplurality of R¹⁷O are present, the plurality of R¹⁷O may represent thesame group or different groups, and the other end having the structurerepresented by general formula (7) or (8):

wherein R²³, R²⁴ and R²⁵ each represent hydrogen atom or a hydrocarbongroup having 1 to 8 carbon atoms, the atoms and the groups representedby R²³, R²⁴ and R²⁵ may be the same with or different from each other,R²⁸, R²⁹, R³⁰ and R³¹ each represent hydrogen atom or a hydrocarbongroup having 1 to 20 carbon atom, the atoms and the groups representedby R²⁸, R²⁹, R³⁰ and R³¹ may be the same with or different from eachother, R²⁶ represents a divalent hydrocarbon group having 1 to 10 carbonatoms, R²⁷ represents a hydrocarbon group having 1 to 20 carbon atoms, qrepresent numbers giving an average value of 0 to 10 and, when aplurality of R²⁶O are present, the plurality of R²⁶O may represent thesame group or different groups; and

Polyvinyl ether compounds which have one end having the structurerepresented by the foregoing general formula (5) or (6) and the otherend having the structure represented by general formula (9):

wherein R³², R³³ and R³⁴ each represent hydrogen atom or a hydrocarbongroup having 1 to 8 carbon atoms and the atoms and the groupsrepresented by R³², R³³ and R³⁴ may be the same with or different fromeach other.

Among the above polyvinyl ether compounds, the following compounds arepreferably used in the present invention:

-   -   (a) Compounds which have one end having the structure        represented by general formula (5) or (6) and the other end        having the structure represented by general formula (7) or (8)        and comprise the structural units represented by general        formula (3) in which R⁵, R⁶ and R⁷ each represent hydrogen        atoms, k represent numbers of 0 to 4, R⁸ represents a divalent        hydrocarbon group having 2 to 4 carbon atoms and R⁹ represents a        hydrocarbon group having 1 to 20 carbon atoms;    -   (b) Compounds which comprise the structural units represented by        general formula (3) alone and have one end having the structure        represented by general formula (5) and the other end having the        structure represented by general formula (7), wherein R⁵, R⁶ and        R⁷ in general formula (3) each represent hydrogen atom, k        represent numbers of 0 to 4, R⁸ represents a divalent        hydrocarbon group having 2 to 4 carbon atoms and R⁹ represents a        hydrocarbon group having 1 to 20 carbon atoms;    -   (c) Compounds which have one end having the structure        represented by general formula (5) or (6) and the other end        having the structure represented by general formula (9) and        comprise the structural units represented by general formula (3)        in which R⁵, R⁶ and R⁷ each represent hydrogen atom, k represent        numbers of 0 to 4, R⁸ represents a divalent hydrocarbon group        having 2 to 4 carbon atoms and R⁹ represents a hydrocarbon group        having 1 to 20 carbon atoms; and    -   (d) Compounds which comprise the structural units represented by        general formula (3) alone and have one end having the structure        represented by general formula (5) and the other end having the        structure represented by general formula (8), wherein R⁵, R⁶ and        R⁷ in general formula (3) each represent hydrogen atom, k        represent numbers of 0 to 4, R⁸ represents a divalent        hydrocarbon group having 2 to 4 carbon atoms and R⁹ represents a        hydrocarbon group having 1 to 20 carbon atoms.

In the present invention, polyvinyl ether compounds which comprise thestructural unit represented by the foregoing general formula (3) andhave one end having the structure represented by the foregoing generalformula (5) and the other end having the structure represented by thefollowing general formula (10):

can also be used. In general formula (10) R³⁵, R³⁶ and R³⁷ eachrepresent hydrogen atom or a hydrocarbon group having 1 to 8 carbonatoms and the atoms and the groups represented by R³⁵, R³⁶ and R³⁷ maybe the same with or different from each other; R³⁸ and R⁴⁰ eachrepresent a divalent hydrocarbon group having 2 to 10 carbon atoms andmay represent the same group or different groups; R³⁹ and R⁴¹ eachrepresent a hydrocarbon group having 1 to 10 carbon atoms and mayrepresent the same group or different groups; c and d each representnumbers giving an average value of 0 to 10 and may represent the samenumber or different numbers; when a plurality of R³⁸O are present, theplurality of R³⁸O may represent the same group or different groups; and,when a plurality of R⁴⁰O are present, the plurality of R⁴⁰O representthe same group or different groups.

Further, examples of the polyvinyl ether compounds which can be used inthe present invention include homopolymers or copolymers of alkyl vinylethers comprising structural units represented by general formula (11)or (12):

wherein R⁴² represents a hydrocarbon group having 1 to 8 carbon atoms,and having a weight-average molecular weight of 300 to 5,000 and one endhaving the structure represented by general formula (13) or (14):

wherein R⁴³ represents an alkyl group having 1 to 3 carbon atoms and R⁴⁴represents a hydrocarbon group having 1 to 8 carbon atoms.

Furthermore, examples of the polyvinyl ether compound described aboveinclude the compounds described in detail in Japanese Patent ApplicationLaid-Open No. Heisei 6(1994)-128578 and Japanese Patent Application Nos.Heisei 5(1993)-125649, Heisei 5(1993)-125650 and Heisei 5(1993)-303736.

The mineral oil component used in the present invention is notparticularly specified. Examples of the mineral oil component includedistilled oils obtained by atmospheric distillation of paraffinic crudeoils, intermediate crude oils and naphthenic crude oils, distilled oilsobtained by vacuum distillation of residual oils of the atmosphericdistillation and purified oils obtained by purifying the above oils inaccordance with a conventional process such as oils purified withsolvents, oils purified by hydrogenation, oils treated by dewaxing andoils treated with white clay. It is suitable that the mineral oilcomponent has a pour point of −5° C. or lower and a content of sulfur of0.01 to 5.00% by weight. When the pour point is higher than −5° C., thepour point of the refrigerating oil composition obtained by mixing withthe polyether compound is elevated and there is the possibility thatfluidity becomes poor. When the content of sulfur is outside the aboverange, there is the anxiety that the effect of addition is not exhibitedor stability deteriorates to cause formation of sludge.

It is necessary that (A):(B), the ratio of the amount by weight ofcomponent (A) comprising the polyether compound to the amount by weightof component (B) comprising the sulfur component, is in the range of25:75 to 99:1. When the ratio is less than the aforementioned range, thesufficient properties cannot be exhibited due to decreases in fluidityat low temperatures and miscibility with ammonia. When the ratio exceedsthe aforementioned range, the effect of addition of the mineral oilcomponent cannot be expected. It is preferable that the ratio is in therange of from 25:75 to 75:25.

It is necessary that the refrigerating oil composition of the presentinvention comprise sulfur components derived from the mineral componentin an amount of 5 to 1,000 ppm and preferably 50 to 500 ppm. Therefore,the amount of the used mineral oil component is adjusted in accordancewith the content of the sulfur components in the mineral oil componentso that the content of sulfur in the refrigerating oil composition isadjusted in the above range. When the content of the sulfur componentsin the refrigerating oil composition is less than 5 ppm, the expectedeffect of the addition to provide the lubricity is not exhibited. Whenthe content of the sulfur components exceeds 1,000 ppm, the stabilitydeteriorates and the fear of formation of sludge increases. To therefrigerating oil composition for natural substance-based refrigerantsof the present invention, where necessary, extreme pressure agents, acidcatchers, antioxidants and anticorrosion agents are added.

In the present invention, the natural substance-based refrigerant meansammonia, propane, butane, carbon dioxide or the like substance. Thelubricating oil composition of the present invention is effective, inparticular, for ammonia-based refrigerants, i.e., refrigerating systemscontaining 90% by weight or more of ammonia. The lubricating oilcomposition of the present invention is also effective for other naturalsubstance-based refrigerating systems. In the process for lubricatingrefrigerators using the refrigerating oil composition of the presentinvention, it is preferable that the ratio of the amount by weight ofthe above natural substance-based refrigerant to the amount by weight ofthe above refrigerating oil composition is in the range of 99/1 to10/90. When the amount of the refrigerant is less than the above range,the refrigerating ability becomes poor. When the amount of therefrigerant exceeds the above range, the lubricity deteriorates.Therefore, amounts outside the above range are not preferable. From theabove standpoint, it is more preferable that the ratio of the amount byweight of the refrigerant to the amount by weight of the refrigeratingoil composition is in the range of 95/5 to 30/70.

The refrigerating oil composition of the present invention can beapplied to various types of refrigerators. In particular, therefrigerating oil composition of the present invention is advantageouslyapplied to compression-type refrigerating cycles in industrialcompression-type refrigerators in which the oil agents and therefrigerant are required in great amounts. For example, therefrigerating oil composition can be advantageously applied torefrigerators disclosed in Japanese Patent Application Laid-Open Nos.Heisei 4(1992)-183788, Heisei 8(1996)-259975, Heisei 8(1996)-240362,Heisei 8(1996)-253779, Heisei 8(1996)-240352, Heisei 5(1993)-17792,Heisei 8(1996)-226717 and Heisei 8(1996)-231972. For example, theadvantageous effects can be exhibited when the refrigerating oilcomposition of the present invention is applied to compression-typerefrigerating cycles having an oil separator and/or a hot gas line suchas the refrigerating cycles shown in FIGS. 1 to 3.

EXAMPLE

The present invention will be described below in further details withreference to the following examples.

The test methods used in the examples were as follows.

[Stability]

Into an autoclave having an inner volume of 20 ml, 7 g of a sample oil,3 g of a refrigerant of ammonia gas and a metal catalyst containingcopper, aluminum and iron were placed and water was added to the systemin an amount such that the content of water was adjusted to 1,000 ppm.After the autoclave was closed and kept at 150° C. for 14 days, thesample oil was analyzed.

[Load of Seizure]

The load of seizure was measured in accordance with the method of ASTMD-3233 with a rotation speed of 290 rpm at the room temperature.

Examples 1 to 5 and Comparative Examples 1 to 5

The test of stability and the measurement of the load of seizure wereconducted using the refrigerating oil compositions shown in Table 1. Theresults are shown in Table 2.

Components (A) and (B) are abbreviated as follows in Table 1.

Component (A) (The synthetic oil component)

-   -   PAG-1; Polyoxypropylene glycol dimethyl ether    -   PAG-2: Polyoxyethylene(10)oxypropylene(90) glycol mono(n-butyl)        ether    -   PAG-3: Polyoxyethylene(20)oxypropylene(80) glycol monoethyl        ether    -   PVE-1: A copolymer of polyethyl vinyl ether (90) and        polyisobutyl vinyl ether (10)    -   PVE-2: A copolymer of polyethyl vinyl ether (70) and        polyisobutyl vinyl ether (30)

Component (B) (The mineral oil component)

-   -   The kinematic viscosity at 40° C.: 11.6 mm²/s    -   The kinematic viscosity at 100° C.: 2.84 mm²/s    -   The content of sulfur: 0.06%    -   The pour point: −45° C.

TABLE 1 Component (A) Composition kinematic kinematic viscosity pourviscosity content at 100° C. point composi- Component (B) at 40° C. ofsulfur type (mm²/s) (° C.) tion composition (mm²/s) (ppm) Example 1PAG-1 17.8 −50> 74 26 49.5 153 Example 2 PAG-2 20.8 −50> 58 42 38.3 255Example 3 PAG-3 25.1 −50> 46 54 31.4 322 Example 4 PVE-1 12.5 −50> 36 6422.4 395 Example 5 PVE-2 11.4 −50> 53 47 32.4 283 Comparative PAG-1 17.8−50> 100 0 99.4   5> Example 1 Comparative PAG-2 20.8 −50> 100 0 129.8  5> Example 2 Comparative PAG-3 25.1 −50> 100 0 160.0   5> Example 3Comparative PVE-1 12.5 −50> 100 0 130.0   5> Example 4 Comparative PVE-211.4 −50> 100 0 113.3   5> Example 5 composition: the ratio of theamount by weight of Component (A) to the amount by weight of Component(B)

TABLE 2 Stability total acid value after Load of appearance precipi-metal test seizure of oil tates catalyst (mgKOH/g) (N) Example 1 goodnone no change 0.01 3560 Example 2 good none no change 0.01 3770 Example3 good none no change 0.01 3650 Example 4 good none no change 0.01 3420Example 5 good none no change 0.01 3370 Comparative good none no change0.01 2890 Example 1 Comparative good none no change 0.01 3060 Example 2Comparative good none no change 0.01 2960 Example 3 Comparative goodnone no change 0.01 2670 Example 4 Comparative good none no change 0.012550 Example 5

INDUSTRIAL APPLICABILITY

In the present invention, the mineral oil component containing sulfur isadded to the synthetic oil component comprising the polyether compoundhaving the specific properties so that the refrigerating oil containssulfur derived from the mineral oil in a specific relative amount. Thelubricity can be improved without adverse effects on compatibility ofthe polyether compound with natural substance-based refrigerants and, inparticular, with ammonia-based refrigerants.

1. A refrigerating oil composition comprising (A) a synthetic oilcomponent having a pour point of −10° C. or lower comprising one or morepolyalkene glycol compounds represented by formula (1):R¹—O-A-R²  (1) wherein one of R¹ or R² is a hydrogen atom and the otherone of R¹ or R² is an alkyl group having 1 to 4 carbon atoms, A is ahomopolymer of propylene oxide or a copolymer of ethylene oxide andpropylene oxide having a number of ethylene oxide units of m and anumber of a propylene oxide units of n, wherein m and n satisfy thefollowing relations:0≦m/n≦10, and5 23 m+n≦100; (B) a purified mineral oil component comprising one ormore sulfur components, wherein the weight ratio (A):(B) is in a rangeof 25:75 to 99:1 and an amount of the sulfur components derived fromcomponent (B) in the composition is in a range of 5 to 1,000 ppm; and(C) ammonia.
 2. A refrigerating oil composition comprising (A) asynthetic oil component having a pour point of −10° C. or lowercomprising one or more polyalkene glycol compounds represented byformula (1):R¹—O-A-R²  (1) wherein one of R¹ or R² is a hydrogen atom and the otherone of R¹ or R² is an alkyl group having 1 to 4 carbon atoms, A is acopolymer of ethylene oxide and propylene oxide having a number ofethylene oxide units of m and a number of a propylene oxide units of n,wherein m and n satisfy the following relations:0≦m/n≦3, and5≦m+n≦100; (B) a purified mineral oil component comprising one or moresulfur components, wherein the weight ratio (A):(B) is in a range of25:75 to 99:1 and an amount of the sulfur components derived fromcomponent (B) in the composition is in a range of 5 to 1,000 ppm; and(C) at least one compound selected from the group consisting of ammonia,propane, butane and carbon dioxide.
 3. A refrigerating oil compositioncomprising (A) a synthetic oil component having a pour point of −10° C.or lower comprising one or more polyalkene glycol compounds representedby formula (1):R¹—O-A-R²  (1) wherein one of R¹ or R² is a hydrogen atom and the otherone of R¹ or R² is an alkyl group having 1 to 4 carbon atoms, A is acopolymer of ethylene oxide and propylene oxide having a number ofethylene oxide units of m and a number of a propylene oxide units of n,wherein m and n satisfy the following relations:  0≦m/n≦2, and5≦m+n≦50; (B) a purified mineral oil component comprising one or moresulfur components, wherein the weight ratio (A):(B) is in a range of25:75 to 99:1 and an amount of the sulfur components derived fromcomponent (B) in the composition is in a range of 5 to 1,000 ppm; and(C) at least one compound selected from the group consisting of ammonia,propane, butane and carbon dioxide.
 4. A refrigerating oil compositioncomprising: (A) polyoxyethylene(10) oxypropylene(90) glycolmono(n-butyl)ether; (B) a purified mineral oil component comprising oneor more sulfur components, wherein the weight ratio (A):(B) is in arange of 25:75 to 99:1 and an amount of the sulfur components derivedfrom component (B) in the composition is in a range of 5 to 1,000 ppm;and (C) at least one compound selected from the group consisting ofammonia, propane, butane and carbon dioxide.
 5. A refrigerating oilcomposition comprising (A) polyoxyethylene(20) oxypropylene(80) glycolmonoethyl ether; (B) a purified mineral oil component comprising one ormore sulfur components, wherein the weight ratio (A):(B) is in a rangeof 25:75 to 99:1 and an amount of the sulfur components derived fromcomponent (B) in the composition is in a range of 5 to 1,000 ppm; and(C) at least one compound selected from the group consisting of ammonia,propane, butane and carbon dioxide.
 6. A refrigerating oil compositioncomprising (A) a copolymer of polyethylvinylether(90) andpolyisobutylvinylether(10); (B) a purified mineral oil componentcomprising one or more sulfur components; and (C) at least one compoundselected from the group consisting of ammonia, propane, butane andcarbon dioxide; wherein the weight ratio (A):(B) is from 25:75 to 99:1,and the amount of the sulfur components derived from component (B) inthe composition is in a range of 5 to 1,000 ppm.
 7. A refrigerating oilcomposition comprising (A) a copolymer of polyethylvinylether(70) andpolyisobutylvinylether(30); (B) a purified mineral oil componentcomprising one or more sulfur components; and (C) at least one compoundselected from the group consisting of ammonia, propane, butane andcarbon dioxide; wherein the weight ratio (A):(B) is from 25:75 to 99:1,and the amount of the sulfur components derived from component (B) inthe composition is in a range of 5 to 1,000 ppm.
 8. A refrigerating oilcomposition comprising (A) a synthetic oil component having a pour pointof −10° C. or lower comprising one or more polyalkene glycol compoundsrepresented by formula (1):R¹—O-A-R²  (1) wherein one of R¹ or R² is a hydrogen atom and the otherone of R¹ or R² is an alkyl group having 1 to 4 carbon atoms, A is ahomopolymer of propylene oxide or a copolymer of ethylene oxide andpropylene oxide having a number of ethylene oxide units of m and anumber of a propylene oxide units of n, wherein m and n satisfy thefollowing relations:  0≦m/n≦10, and5≦m+n≦100; (B) a purified mineral oil component comprising one or moresulfur components, wherein the weight ratio (A):(B) is in a range of25:75 to 99:1 and an amount of the sulfur components derived fromcomponent (B) in the composition is in a range of 5 to 1,000 ppm; and(C) propane.
 9. A refrigerating oil composition comprising (A) asynthetic oil component having a pour point of −10° C. or lowercomprising one or more polyalkene glycol compounds represented byformula (1):R¹—O-A-R²  (1) wherein one of R¹ or R² is a hydrogen atom and the otherone of R¹ or R² is an alkyl group having 1 to 4 carbon atoms, A is ahomopolymer of propylene oxide or a copolymer of ethylene oxide andpropylene oxide having a number of ethylene oxide units of m and anumber of a propylene oxide units of n, wherein m and n satisfy thefollowing relations:0≦m/n≦10, and5≦m+n≦100; (B) a purified mineral oil component comprising one or moresulfur components, wherein the weight ratio (A):(B) is in a range of25:75 to 99:1 and an amount of the sulfur components derived fromcomponent (B) in the composition is in a range of 5 to 1,000 ppm; and(C) butane.
 10. A refrigerating oil composition comprising (A) asynthetic oil component having a pour point of −10° C. or lowercomprising one or more polyalkene glycol compounds represented byformula (1):R¹—O-A-R²  (1) wherein one of R¹ or R² is a hydrogen atom and the otherone of R¹ or R² is an alkyl group having 1 to 4 carbon atoms, A is acopolymer of ethylene oxide and propylene oxide having a number ofethylene oxide units of m and a number of a propylene oxide units of n,wherein m and n satisfy the following relations:0≦m/n≦10, and5≦m+n≦100; (B) a purified mineral oil component comprising one or moresulfur components, wherein the weight ratio (A):(B) is in a range of25:75 to 99:1 and an amount of the sulfur components derived fromcomponent (B) in the composition is in a range of 5 to 1,000 ppm; and(C) at least one compound selected from the group consisting of ammonia,propane, butane and carbon dioxide.
 11. A refrigerating oil compositioncomprising (A) one or more polyvinyl ether compounds; (B) a purifiedmineral oil component comprising one or more sulfur components; and (C)ammonia; wherein the weight ratio (A):(B) is from 25:75 to 99:1, and theamount of the sulfur components derived from component (B) in thecomposition is in a range of 5 to 1,000 ppm.